Utilize C version of CommonMark renderer

Originally we used the Ruby version, which gave us
additional flexibility to handle a special case.
We've now refactored that out and can use the
C version, which is much more performant over
the Ruby version

Changelog: performance

config/feature_flags/development/use_cmark_renderer.yml

@@ -5,4 +5,4 @@ rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/345744
 milestone: '14.6'
 type: development
 group: group::project management
-default_enabled: false
+default_enabled: true